checkout: always set the index in checkout data

Always set the `index` in the `checkout_data`, even in the case that we
are not reloading the index.  Other functionality in checkout examines
the index (for example: determining whether the workdir is modified) and
we need it even in the (uncommon) case that we are not reloading.

src/checkout.c

@@ -2397,6 +2397,9 @@ static int checkout_data_init(
 				GIT_DIR_MODE, GIT_MKDIR_VERIFY_DIR)) < 0)
 		goto cleanup;
 
+	if ((error = git_repository_index(&data->index, data->repo)) < 0)
+		goto cleanup;
+
 	/* refresh config and index content unless NO_REFRESH is given */
 	if ((data->opts.checkout_strategy & GIT_CHECKOUT_NO_REFRESH) == 0) {
 		git_config *cfg;
@@ -2404,13 +2407,10 @@ static int checkout_data_init(
 		if ((error = git_repository_config__weakptr(&cfg, repo)) < 0)
 			goto cleanup;
 
-		/* Get the repository index and reload it (unless we're checking
-		 * out the index; then it has the changes we're trying to check
-		 * out and those should not be overwritten.)
+		/* Reload the repository index (unless we're checking out the
+		 * index; then it has the changes we're trying to check out
+		 * and those should not be overwritten.)
 		 */
-		if ((error = git_repository_index(&data->index, data->repo)) < 0)
-			goto cleanup;
-
 		if (data->index != git_iterator_index(target)) {
 			if ((error = git_index_read(data->index, true)) < 0)
 				goto cleanup;